Understanding the characteristics of geologic formations and fluids located therein is important for effective hydrocarbon exploration and production. Formation evaluation relies on accurate petrophysical interpretation derived from a diverse set of logging technologies. One such technology, nuclear magnetic resonance (NMR), can be used to estimate formation characteristics such as mineralogy-independent porosity and permeability of rocks, to perform fluid typing and determine fluid volumes, and to estimate fluid characteristics such as viscosity.
Various properties of formations can be derived from NMR measurements, such as porosity, volumetrics, permeability, saturation, viscosity, fluid type and pore size distribution. Sourceless porosity is an important trend in formation evaluation, and NMR logging is considered to be a potential replacement of the standard density-neutron approach to measure formation porosity. One major difficulty of NMR logging is to provide accurate porosity in a gas reservoir, and the conventional wisdom is that standalone low-gradient NMR logging tools are not appropriate for logging in light oil and gas reservoirs.